How to MegaSquirt Your Chrysler, Dodge, or Mitsubishi 3.0 SOHC

Using the stock distributor Updated 1/19/2009Application(s): This article covers the 1988-1995 Mitsubishi / Dodge / Chrysler 3.0 SOHC V6, as used in K-car derived cars (Daytona, LeBaron, Shadow, Sundance, minivans, and other applications) as well as in the Mitsubishi Diamante and various Mitsubishi trucks.

Level of control: Parallel installation — Fuel and Ignition Control. Most users will want to retain the stock computer for things like alternator control, although the Megasquirt is close to acting as a full standalone EMS. For parallel installation tips, see this article.

The 3.0 SOHC V6 was a joint venture between Chrysler and Mitsubishi, and is a straightforward engine to MegaSquirt. These engines used a basic optical distributor with two rows of trigger holes. One row, called the low data rate, consists of six equally spaced slots. The other one, called the high data rate, usually contained 360 equally spaced slots except it had 10 consecutive slots missing, making it a 360-10 wheel instead of the common 36-1. A few applications used a row of 4 unequally sized slots in place of the high data rate slots. However, in either case, MegaSquirt only needs the signal from the 6 equally spaced ‘low data rate’ slots.

ECU Modifications

With this engine, we recommend MegaSquirt-II. Its stepper IAC motor control can drive the stock idle air control valve, which is one feature MegaSquirt-I does not have. For those looking to build this on a budget and willing to find another way to control idle or give up idle control entirely, we also have a write-up covering MegaSquirt-I.

Using the MS-II PCBv3 or V3.57 ECU

In step 22, install the stepper IAC jumpers (all of our MS230-C and MS2357-C units are by default configured this way).

Build the ECU up to trigger from the Hall/Optical Input (all of our MS230-C and MS2357-C units are by default configured this way, too.).

We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect (for a V3.0 board) or pin 3 of the JP1 jumper (for a V3.57 board). It’s best to wrap this resistor in heat shrink tubing and put it on the underside of the board.

The only change is to enable the IGBT High Current Ignition Coil Driver Circuit to directly drive the coil. (If you’re buying an assembled unit, we’ll gladly do this for you for just a few bucks, shoot us an email)

Remove the jumper from JS10 to IGN (on a V3.0 board) or from JS10 to the center hole of Q16 (V3.57) Some MegaSquirts may not have this jumper installed.

Jumper IGBTIN to JS10

Jumper IGBTOUT to IGN (on a V3.0 board)

If Q16 is not fitted, install a BIP373 in the Q16 slot using a mica insulator.

(This will enable the BIP373 Ignition Coil Driver)

That’s it!

Using the MS-I PCBv3 with MSnS-E firmware

Note the separate instructions for v3.0 and v3.57 PCBs

This will let you control fuel and ignition, but not the IAC valve.

MegaSquirt-I PCBv3.0 Mods Required:

This is assuming you are starting with an ECU built up like I build my assembled MS130-C MegaSquirt-I PCB3.0 units. If you are building your unit up from a kit you can implement these changes during assembly.

We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and TachSelect. Wrapping the resistor in heat shrink tubing will protect it from accidental shorts.

Jumper IGBTOUT to IGN to send to IGBT ignition coil driver signal out of pin 36 on the DB37.

Cut out C12 and C30. (Only needed when triggering from the – terminal of the coil, which you are not)

Remove D1 and jumper it, or just install a jumper wire across it’s leads. (Only needed when triggering from the – terminal of the coil, which you are not)

Cut out R57 if fitted (this won’t be there on my units though).

Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.

Tin each end of the resistor with a bit of solder.

Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.

Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.

Heatshrink wrap this wire/resistor assembly.

Use this wire/resistor combo to jumper the ‘top’ (top as in when you facing the silkscreen side of the PCB, with the text so that you can read it normally) lead of R26 to IGBTIN on the opposite side of the PCB.

MegaSquirt-I PCBv3.57 Mods Required: \

We will need a 12 volt pull up on the ignition input. Solder a 1K resistor between S12 and pin 3 of the JP1 jumper (for a V3.57 board). It’s best to wrap this resistor in heat shrink tubing and put it on the underside of the board.

Get a 330 ohm 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.

Tin each end of the resistor with a bit of solder.

Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.

Melt the tinned wire tip to one end of the tinned 330 ohm resistor tip and let it cool.

Heatshrink wrap this wire/resistor assembly.

Run this resistor on a wire combination from the right side of R26 (I know, it’s kind of tough to solder to a surface mount resistor) or pin 7 of the Ul socket (which is a lot easier to solder to) over to IGBTIN.

Install a BIP373 transistor in the Q16 slot, using a mica insulator.

That’s it!

Wiring

The output is quite straightforward – you will just need to connect the negative terminal of the coil to pin 36. The positive terminal is connected to the same switched power source used with the stock ECU. For the input side, wire the low resolution input signal from the low data rate output pin to the MegaSquirt pin 24.

Optical pickup pin out

Pin

Purpose

1

Low data rate (MS Pin 24)

2

High data rate (Not used)

3

12 volt power

4

Ground

Idle Air Control

These engines used a stepper idle air control motor. Chrysler versions used a 4 pin unipolar motor, while the Mitsubishi version has a six pin bipolar motor. Using the bipolar motor requires disconnecting its 12 volt power feed line. If you have a MegaSquirt-II, you can drive the IAC valve from the MegaSquirt pins 25, 27, 29, and 31. Chrysler used a couple different pinouts for IAC valves on these engines; early ones usually use the top version in this drawing, while later ones usually use the middle version.

For the version installed in the Mitsubishi models, we have the pinout information for the 6 wire IAC, but haven’t yet determined the exact polarity of the wiring yet. We’re confident we can work through it with a volunteer customer that’s diving into this and we’ll update this article then; just let us know and we’ll work through it with you.

Other Things the ECU Controls

The stock ECU controls a couple other devices in these cars besides the injectors, ignition, and IAC valve. Here’s what to do about the ones you will need to control.

Fuel pump: This is a standard output on the Megasquirt. Wire the Megasquirt pin 37 to the fuel pump relay wire that went to the stock ECU.

Cooling fans: The ECU has a single cooling fan output. On the MS2, you can use the on/off IAC output to drive the cooling fan relay. On a MS1, you’ll want to add a MK-RelayCtrl for this.

Alternator voltage: These cars have the voltage regulator built into the ECU. We recommend leaving the stock ECU in place in a parallel installation so it can still control this. The other option would be converting to an external voltage regulator.

Air conditioning: While the stock ECU controls the air conditioner, you don’t need a computer to make this work. Wiring the A/C request wire running to the ECU to the A/C compressor relay should make this work, although if you are leaving the stock ECU to control the alternator, you might as well leave it to control the A/C as well.

Automatic transmission: The 41TE has its own controls, but they often talk to the stock ECU. If you have these, this is yet another good reason for a parallel install.

If you are leaving the stock computer in control of anything, it’s best to give the Megasquirt its own temperature sensors, as sharing these with the stock ECU is tricky.

TunerStudio Configuration for MS-II

Set ignition capture to “Falling Edge,” and coil charging to Standard Coil Charging. Dwell will depend on exactly which coil you are using. Cranking trigger time must be set to Calculated. If using MS2/Extra, set the ignition type to Basic Trigger.

Important when using the BIP373: On the ‘Ignition Settings’ menu make sure to set ‘Spark Output’ to ‘Going High (Inverted)’ and set ‘Coil Charging Scheme’ to ‘Standard Coil Charge’.

If you use someone else’s .msq file we do recommend you check the firmware version the .msq file was built on as you cannot always use a file built on one firmware version with an ECU running a different version– it’s best to use the .msq files with the same version of the firmware that the file was built on. Alternately you can manually copy the settings over from the borrowed file.

MegaTune Configuration for MS1 Extra

On the ‘Spark’ menu choose ‘Spark Settings’ and set ‘Spark Output Inverted’ to YES. It is critical to get the Spark Output Inverted setting correct, as setting this wrong can result in damage to the BIP373 or coil. Dwell settings will depend on the coil used. A typical rule of thumb is to back off the dwell until you can just barely detect a misfire under lean cruising conditions, then add 0.2 ms of dwell time.

If you use someone else’s .msq file we do recommend you check the firmware version the .msq file was built on as you cannot always use a file built on one firmware version with an ECU running a different version– it’s best to use the .msq files with the same version of the firmware that the file was built on. Alternately you can manually copy the settings over from the borrowed file.

Suggested parts

As stated above, we recommend a MegaSquirt-II V3.0 or V3.57 to have full control over the engine. You will be able to use your existing sensors except for the MAP sensor which is built into the MegaSquirt if you are removing the stock computer. If you are leaving the stock computer in place, we recommend adding a coolant temperature sensor and an IAT sensor for the Megasquirt.

Making Your Order Easy

We’ve taken the above list of suggestions a step further, and used it to create two single part#’s you can order by to get everything you need, either in kit or assemble form. So all you need to answer is, are you a hardcore DIY Build-It-Yourself from a kit kind of guy? Or would you like it to arrive prebuilt, with all hardware mods completed, and ready to wire up with all the accessories you’ll need?

Note we left a Wideband O2 System OUT of these packages to keep your initial cost down, but as with any engine management system you’ll definitely appreciate a wideband system during tuning. We highly recommend the Innovate LC-1 with or without a gauge.